LANCASTER, N.H. — Jeanne and Andy Nadeau had one gnawing question about their large family: would the hearing loss that affects half of their busy, boisterous household of 10 children worsen as they grew older?

The Nadeaus could prepare for the future if they knew whether the children who whisper in shouting voices and sleep soundly through violent thunderstorms would eventually become deaf or develop other health issues. Jeanne could make sure they learned sign language.

But genetic tests had been inconclusive. So, two years ago, when the parents were asked to participate in a study that would more broadly examine their family’s genes, using a nascent technology called whole genome sequencing, they were interested.

The technology has begun to shift from a tool used primarily in research to a medical test.